There have been over 200 documented cases of jet engine power loss events during flight at high altitudes due to ingestion of ice particles. The events typically occur at altitudes above 22,000 feet and near deep convective systems, often in tropical regions. It is recognized in the industry that supercooled liquid water does not exist in large quantities at these high altitudes and therefore it is expected that the events are due to the ingestion of ice particles.
Based on this recent interest in ice particle threat to engines in flight, the NASA Glenn Research Center (GRC) installed the capability to produce ice crystal and mixed phase water clouds in the Propulsion Systems Laboratory (PSL) Test Cell 3. The ice crystal cloud operational parameters, developed with input from industry, were Median Volumetric Diameter (MVD) from 40 to 60 pm and Total Water Content (TWC) from 0.5 to 9.0 g/m3. The PSL is currently the only engine test facility that can simulate both altitude effects and an ice crystal cloud. It is a continuous flow facility that creates the temperature and pressure inlet conditions that propulsion systems experience in high-speed, high-altitude flight. Specifically for the icing system, the total temperature can be controlled between +45 to −60 F, pressure altitude from 4,000 to 40,000 feet (facility limit is 90,000 feet), and Mach from 0.15 to 0.8 (facility limit is Mach 3.0).
Within this facility, there was a specific need to develop a non-intrusive system to measure the conditions of a cloud that enters an aircraft engine in the PSL. The system should (1) have the capability to be operated remotely, (2) have minimal optical access, (3) no moving parts, (4) fast acquisition and (5) good resolution in a pipe that can structurally support an aircraft engine in close proximity. An earlier study of this problem is described in “Application of the Radon Transform to Calibration of the NASA-Glenn Icing Research Wind Tunnel,” by Izen, S H, and Bencic, T J, in Contemporary Mathematics, Vol. 278, 2001, pp. 147-166.